1. Field of the Invention
The present invention relates to a collinear dipole antenna and communication device, and more particularly, to a collinear dipole antenna and communication device whose arms with positive current phase having a bishop-hat shape and arms with negative current phase having a meandering shape.
2. Description of the Prior Art
New generation Wi-Fi communication system utilizes beam forming technique to form either an omni-directional pattern or a directional pattern, wherein the omni-directional and directional patterns can be synthesized by combining multiple collinear antennas, wherein the collinear antennas are omni-directional with high gain. There are various types for collinear antennas, one of which is formed by dipole antennas.
Operations of the collinear dipole antenna are described in the following description. FIG. 1 is a schematic diagram of a collinear dipole antenna 10. The collinear dipole antenna 10 includes radiators 11 and 12, a feed terminal 103, and a substrate 104. The radiators 11 and 12 may be formed on the substrate 104. The radiator 11 is electrically connected to the feed terminal 103 to receive a radio signal (generated by a radio signal processing unit not shown in FIG. 1) via the feed terminal 103. The radiator 12 is electrically connected to a ground.
FIG. 1 further illustrates wavelengths and current phases corresponding to an operating frequency of the radiators 11 and 12. In general, in order to increase an antenna gain on horizontal sections, a total length of the radiators 11 and 12 may be N wavelengths plus a quarter-wavelength of the operating frequency, where N is an integer. A same boundary condition at open ends of the radiators 11 and 12 is reserved since intensities of the currents flowing on the radiators 11 and 12 repeat at every wavelength and the intensities of currents are zero at the quarter-wavelength. Therefore, the radiators 11 and 12 can satisfy a same resonance requirement due to the same boundary condition, i.e., currents on the radiators 11 and 12 are always zero at the open ends.
The antenna gain on the horizontal section is positively correlated with current components with positive phases, while the antenna gain on the horizontal section is negatively correlated with current components with negative phases. As can be seen from a current phase distribution of the collinear dipole antenna 10, the antenna gain is decreased due to the current components with negative phases. In addition, there are issues for the collinear dipole antenna 10 needed to be solved such as insufficient bandwidth and dramatically gain drop within the bandwidth.
Therefore, how to improve the antenna performance of the collinear dipole antenna, such as increasing the antenna gain, broadening the bandwidth and smoothing the gain drop within the bandwidth, has become a topic in the industry.